Polyurethane polymers are conventionally prepared by the reaction of an organic polyol, such as a polyether or polyester polyol, with a polyisocyanate. The rate of the reaction is controlled by adding catalysts such as triethylamine, triethylene diamine or other amine catalysts. Other optional ingredients in the foam formulation include blowing agent(s), surfactant(s) and flame retardant(s).
Rigid polyurethane foams can be made of polyether polyols that are prepared using sucrose, sorbitol and methylglucoside. Sucrose is the preferred sugar for this purpose because of its availability and low cost.
The milk sugar, lactose, has also been shown to be usable in making polyurethane foams. Whey powder, containing lactose as the polyhydroxy compound, in DMSO, has been used in conjunction with polyisocyanate, catalyst and blowing agent to make polyurethane foams, Richardson et al. U.S. Pat. No. 3,658,731. The foams, however, have highly opened cell structures and low compressive strength.
The DMSO can be omitted from the formula when the whey substitution is limited to about 80% (preferably in the range of 50-60%)--the remaining being a conventional sucrose-based polyol, Richardson et al. U.S. Pat. No. 3,629,162. However, the properties of the product are inferior to the foams prepared from formulations using no lactose additives. In addition, polyol formulations using insoluble lactose additives are highly susceptible to settling and abrasive to mixing head, pumps and pressure regulating valves of dispensing equipments.
The substitution of lactose for sucrose in propoxylation reactions leads to side reactions as the result of the action of the required base and heat on lactose. These side reactions result in dark polyol preparations. The crude lactose-based polyol preparations are high in carbonyl content--a feature that was made use of in the covalent incorporation of urea in the polyol preparation by heating the two ingredients together. The polyurethane foams prepared using urea-modified polyethers exhibit improved flame-retardant qualities over conventional sucrose based foams, Richardson et al. U.S. Pat. No. 4,459,397.
Other patents suggest that urea be mixed mechanically with polyurethane foams to produce self-extinguishing foams. For example, the Hesskamp, U.S. Pat. No. 3,717,597 discloses a self-extinguishing composite material including bits of polyurethane foam mechanically mixed with urea and bound together to form a self-extinguishing composite material.
Difficulties have been encountered when attempts have been made to incorporate solid urea in conventional polyols prior to mixing with isocyanate to form the polyurethane polymer. The dispersed granular urea in the liquid polyol leads to abrasion and increased wear of pumps, pipes and nozzles used to dispense the material. The Reymore, et al. U.S. Pat. No. 3,420,787 and Richter, et al. U.S. Pat. No. 4,154,931 disclose methods of incorporating substituted ureas and cyclic ureas as extenders in polyurethane formulations for making polyurethane foams having improved flame retardancy.
It obviously would be desirable to have improved polyols which contain high concentrations of urea from which to make polyurethane foams of superior flame retardancy.